Jim Gates: What is Supersymmetry?

00:00:00.000 | - Some of the fascinating work you've done

00:00:04.080 | is in the space of supersymmetry, symmetry in general.

00:00:09.080 | Can you describe first of all what is supersymmetry?

00:00:12.400 | - Ah yes, so you remember the two buckets I told you about,

00:00:15.560 | perhaps earlier, so there are two buckets in our universe.

00:00:19.240 | So now I want you to think about drawing a pie

00:00:24.240 | that has four quadrants, so I want you to cut

00:00:26.880 | the piece of pie in fourths.

00:00:29.320 | So in one quadrant I'm gonna put all the buckets

00:00:31.400 | that we talked about that are like the electron

00:00:33.640 | and the quarks, in a different quadrant I am going

00:00:36.080 | to put all the force carriers.

00:00:37.660 | The other two quadrants are empty.

00:00:39.740 | Now if you, I showed you a picture of that,

00:00:41.680 | you'd see a circle, there would be a bunch of stuff

00:00:44.400 | in one upper quadrant and stuff in others,

00:00:47.040 | and then I would ask you a question.

00:00:49.080 | Does that look symmetrical to you?

00:00:50.780 | - No.

00:00:53.040 | - No, and that's exactly right because we humans

00:00:56.000 | actually have a very deeply programmed sense of symmetry.

00:01:01.000 | It's something that is part of that mystery of the universe.

00:01:06.080 | So how would you make it symmetrical?

00:01:07.600 | One way you could is by saying those two empty quadrants

00:01:10.140 | had things in them also, and if you do that,

00:01:14.100 | that's supersymmetry.

00:01:15.680 | So that's what I understood when I was a graduate student

00:01:18.220 | here at MIT in 1975, when the mathematics of this

00:01:23.160 | was first being born.

00:01:25.480 | Supersymmetry was actually born in the Ukraine

00:01:28.240 | in the late '60s, but we had this thing called

00:01:30.120 | the Iron Curtain, so we Westerners didn't know about it.

00:01:33.720 | But by the early '70s, independently,

00:01:36.080 | there were scientists in the West who had rediscovered

00:01:38.560 | supersymmetry, Bruno Zemino and Julius Vest

00:01:42.160 | were their names.

00:01:43.620 | So this was around '71 or '72 when this happened.

00:01:47.360 | I started graduate school in '73, so around '74, '75,

00:01:51.640 | I was trying to figure out how to write a thesis

00:01:53.320 | so that I could become a physicist the rest of my life.

00:01:56.800 | I had a great advisor, Professor James Young,

00:02:00.880 | who had taught me a number of things about electrons

00:02:04.320 | and weak forces and those sorts of things.

00:02:07.160 | But I decided that if I was going to have a really,

00:02:12.160 | an opportunity to maximize my chances of being successful,

00:02:18.680 | I should strike it out in a direction that other people

00:02:20.680 | were not studying.

00:02:21.960 | And so as a consequence, I surveyed ideas

00:02:25.440 | that were being developed, and I came across the idea

00:02:28.560 | of supersymmetry.

00:02:30.240 | And it was so, the mathematics was so remarkable

00:02:33.880 | that I just, it bowled me over.

00:02:36.280 | I actually have two undergraduate degrees.

00:02:38.640 | My first undergraduate degree is actually mathematics,

00:02:40.740 | and my second is physics, even though I always wanted

00:02:44.040 | to be a physicist.

00:02:45.220 | Plan A, which involved getting good grades, was mathematics.

00:02:50.720 | I was a mathematics major thinking about graduate school,

00:02:53.720 | but my heart was in physics.

00:02:55.200 | - If we could take a small digression,

00:02:59.440 | what's to you the most beautiful idea in mathematics

00:03:02.280 | that you've encountered in this interplay

00:03:04.760 | between math and physics?

00:03:06.600 | - It's the idea of symmetry.

00:03:08.680 | The fact that our innate sense of symmetry winds up

00:03:13.680 | aligning with just incredible mathematics,

00:03:17.720 | to me, is the most beautiful thing.

00:03:20.640 | It's very strange but true that if symmetries were perfect,

00:03:24.840 | we would not exist.

00:03:26.360 | And so even though we have these very powerful ideas

00:03:28.480 | about balance in the universe in some sense,

00:03:30.920 | it's only when you break those balances

00:03:32.400 | that you get creatures like humans

00:03:34.200 | and objects like planets and stars.

00:03:36.800 | So although they are a scaffold for reality,

00:03:40.280 | they cannot be the entirety of reality.

00:03:42.720 | So I'm kind of naturally attracted to parts of physics

00:03:47.840 | and attracted to parts of science and technology

00:03:52.160 | where symmetry plays a dominant role.

00:03:54.640 | - And not just, I guess, symmetry as you said,

00:03:56.720 | but the magic happens when you break the symmetry.

00:04:00.040 | - The magic happens when you break the symmetry.

00:04:02.800 | - Okay, so diving right back in,

00:04:04.480 | you mentioned four quadrants.

00:04:06.320 | - Yes.

00:04:07.280 | - Two are filled with stuff, two buckets.

00:04:10.360 | And then there's crazy mathematical thing,

00:04:12.680 | ideas for filling the other two.

00:04:14.840 | What are those things?

00:04:16.560 | - So earlier, the way I described these two buckets

00:04:19.440 | is I gave you a story that started out

00:04:22.160 | by putting us in a dusty room with two flashlights.

00:04:25.920 | And I said, "Turn on your flashlight, I'll turn on mine.

00:04:28.480 | "The beams will go through each other."

00:04:30.120 | And the beams are composed of force carriers called photons.

00:04:34.200 | They carry the electromagnetic force.

00:04:36.480 | And they pass right through each other.

00:04:37.600 | So imagine looking at the mathematics of such an object,

00:04:40.840 | which you don't have to imagine people like me do that.

00:04:44.640 | So you take that mathematics,

00:04:46.000 | and then you ask yourself a question.

00:04:48.400 | You see, mathematics is a palette.

00:04:49.880 | It's just like a musical composer

00:04:53.880 | is able to construct variations on a theme.

00:04:57.640 | Well, a piece of mathematics in the hand of a physicist

00:05:00.000 | is something that we can construct variations on.

00:05:02.240 | So even though the mathematics that Maxwell gave us

00:05:06.480 | about light, we know how to construct variations on that.

00:05:11.360 | And one of the variations you can construct

00:05:13.480 | is to say, suppose you have a force carrier

00:05:15.800 | for electromagnetism that behaves like an electron

00:05:20.400 | in that it would bounce off of another one.

00:05:22.480 | That's changing a mathematical term in an equation.

00:05:26.400 | So if you did that, you would have a force carrier.

00:05:29.840 | So you would say, first,

00:05:31.080 | it belongs in this force-carrying bucket.

00:05:32.840 | But it's got this property of bouncing off like electrons.

00:05:34.920 | So you say, well, gee, wait, no,

00:05:36.520 | that's not the right bucket.

00:05:37.720 | So you're forced to actually put it

00:05:38.880 | in one of these empty quadrants.

00:05:40.920 | So those sorts of things, basically, we give them,

00:05:45.200 | so the photon mathematically can be accompanied by a photino.

00:05:49.040 | It's the thing that carries a force

00:05:51.320 | but has the rule of bouncing off.

00:05:52.960 | In a similar manner, you could start with an electron.

00:05:57.360 | And you say, okay, so write down

00:05:58.840 | the mathematics of an electron.

00:06:00.120 | I know how to do that.

00:06:01.320 | A physicist named Dirac first told us how to do that

00:06:03.320 | back in the late '20s, early '30s.

00:06:06.600 | So take that mathematics, and then you say,

00:06:08.400 | let me look at that mathematics

00:06:10.800 | and find out what in the mathematics

00:06:12.720 | causes two electrons to bounce off of each other,

00:06:15.360 | even if I turn off the electrical charge.

00:06:17.640 | So I could do that.

00:06:18.720 | And now let me change that mathematical term.

00:06:21.320 | So now I have something that carries electrical charge,

00:06:23.800 | but if you take two of them,

00:06:25.440 | I'm sorry, if you turn their charges off,

00:06:26.800 | they'll pass through each other.

00:06:28.480 | So that puts things in the other quadrant.

00:06:30.760 | And those things we tend to call,

00:06:32.800 | we put the S in front of their name.

00:06:35.680 | So in the lower quadrant here, we have electrons.

00:06:37.960 | In this now newly filled quadrant, we have electrons.

00:06:41.320 | In the quadrant over here, we had quarks.

00:06:45.440 | Over here, we have squarks.

00:06:46.880 | So now we've got this balanced pi,

00:06:48.720 | and that's basically what I understood

00:06:50.720 | as a graduate student in 1975

00:06:53.640 | about this idea of supersymmetry,

00:06:55.560 | that it was going to fill up these two quadrants

00:06:57.520 | of the pi in a way that no one

00:06:59.040 | had ever thought about before.

00:07:00.920 | So I was amazed that no one else at MIT

00:07:03.360 | found this an interesting idea.

00:07:05.520 | So it led to my becoming the first person

00:07:08.960 | in MIT to really study supersymmetry.

00:07:12.680 | This is 1975, '76, '77.

00:07:15.800 | And in '77, I wrote the first PhD thesis

00:07:18.040 | in the physics department on this idea

00:07:20.280 | because I was drawn to the balance.

00:07:22.800 | - Drawn to the symmetry.

00:07:24.720 | So what does that, first of all,

00:07:29.720 | is this fundamentally a mathematical idea?

00:07:34.440 | So how much experimental,

00:07:36.720 | and we'll have this theme,

00:07:37.560 | it's a really interesting one.

00:07:38.800 | When you explore the world of the small,

00:07:41.400 | and in your new book talking about

00:07:44.440 | Approving Einstein, right, that we'll also talk about,

00:07:47.320 | there's this theme of kind of starting it,

00:07:49.880 | exploring crazy ideas first in the mathematics,

00:07:52.760 | and then seeking for ways to experimentally validate them.

00:07:56.280 | Where do you put supersymmetry in that?

00:07:58.840 | - It's closer than string theory.

00:08:01.520 | It has not yet been validated.

00:08:03.980 | In some sense, you mentioned Einstein,

00:08:06.480 | so let's go there for a moment.

00:08:08.720 | In our book, Proving Einstein Right,

00:08:10.340 | we actually do talk about the fact

00:08:12.120 | that Albert Einstein in 1915 wrote a set of equations

00:08:16.240 | which were very different from Newton's equations

00:08:18.440 | in describing gravity.

00:08:20.120 | These equations made some predictions

00:08:22.240 | that were different from Newton's predictions.

00:08:24.560 | It actually made three different predictions.

00:08:26.400 | One of them was not actually a prediction,

00:08:28.400 | but a postdiction because it was known

00:08:30.360 | that Mercury was not orbiting the sun

00:08:32.800 | in the way that Newton would have told you.

00:08:34.900 | And so Einstein's theory actually describes Mercury orbiting

00:08:39.140 | in the way that it was observed

00:08:41.500 | as opposed to what Newton would have told you.

00:08:43.100 | So that was one prediction.

00:08:44.900 | The second prediction that came out

00:08:46.560 | of the theory of general relativity,

00:08:47.960 | which Einstein wrote in 1915,

00:08:50.680 | was that if you,

00:08:53.640 | so let me describe an experiment and come back to it.

00:08:57.860 | Suppose I had a glass of water,

00:08:59.940 | and I filled the glass up,

00:09:03.380 | and then I moved the glass slowly back and forth

00:09:05.480 | between our two faces.

00:09:07.260 | It would appear to me like your face was moving,

00:09:11.000 | even though you weren't moving.

00:09:12.240 | I mean, it's actually, and what's causing it

00:09:14.440 | is because the light gets bent through the glass

00:09:16.780 | as it passes from your face to my eye.

00:09:19.540 | So Einstein, in his 1915 theory of general relativity,

00:09:24.540 | found out that gravity has the same effect on light

00:09:28.620 | as that glass of water.

00:09:29.660 | It would cause beams of light to bend.

00:09:32.420 | Now, Newton also knew this,

00:09:35.180 | but Einstein's prediction was that light

00:09:36.900 | would bend twice as much.

00:09:38.940 | And so here's a mathematical idea.

00:09:41.460 | Now, how do you actually prove it?

00:09:43.140 | Well, you've got to watch, yes.

00:09:45.900 | - Just a quick pause on that,

00:09:47.340 | just the language you're using.

00:09:48.900 | He found out.

00:09:51.000 | - I can say he did a calculation.

00:09:52.780 | - It's a really interesting notion

00:09:54.380 | that one of the most,

00:09:56.220 | one of the beautiful things about this universe

00:09:58.340 | is you can do a calculation

00:10:01.140 | and combine with some of that magical intuition

00:10:04.100 | that physicists have,

00:10:05.500 | actually predict what would be,

00:10:08.420 | what's possible to experiment to validate.

00:10:10.820 | - That's correct.

00:10:11.640 | - So he found out in the sense that

00:10:13.660 | there seems to be something here

00:10:16.500 | and mathematically it should bend,

00:10:19.220 | gravity should bend light this amount.

00:10:21.700 | And so therefore that's something that could be potentially,

00:10:24.540 | and then come up with an experiment that could be validated.

00:10:26.540 | - Right.

00:10:27.580 | And that's the way that actually modern physics,

00:10:30.500 | deeply fundamental modern physics,

00:10:33.060 | this is how it works.

00:10:34.160 | Earlier we spoke about the Higgs boson.

00:10:37.620 | So why did we go looking for it?

00:10:39.220 | The answer is that back in the late 60s, early 70s,

00:10:45.140 | some people wrote some equations

00:10:47.020 | and the equations predicted this.

00:10:49.780 | So then we went looking for it.

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